Optical devices are known that can change the transmission state of external light entering from outside, such as sunlight.
For example, PTL 1 discloses a reflection dimmer that can be used in a window material for architectural structures. The reflection dimmer disclosed in PTL 1 includes a pair of transparent electrodes and an optical function layer retained between the transparent electrodes. The optical function layer includes an irregular transparent surface layer having a plurality of recesses in the surface, and a liquid crystal material filled in each recess. The reflection dimmer can refract or reflect incident light or allow incident light to directly pass through by changing a difference in refractive index between the liquid crystal material and the irregular transparent surface layer in response to an electric field applied between the transparent electrodes.